Additional minor cleanup regarding CallWrapper: Use the null object pattern.

src/ia32/macro-assembler-ia32.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 139 matching lines @@
   void LoadFromSafepointRegisterSlot(Register dst, Register src);
 
   // ---------------------------------------------------------------------------
   // JavaScript invokes
 
   // Invoke the JavaScript function code by either calling or jumping.
   void InvokeCode(const Operand& code,
                   const ParameterCount& expected,
                   const ParameterCount& actual,
                   InvokeFlag flag,
-                  CallWrapper* call_wrapper = NULL);
+                  const CallWrapper& call_wrapper = NullCallWrapper());
 
   void InvokeCode(Handle<Code> code,
                   const ParameterCount& expected,
                   const ParameterCount& actual,
                   RelocInfo::Mode rmode,
                   InvokeFlag flag,
-                  CallWrapper* call_wrapper = NULL);
+                  const CallWrapper& call_wrapper = NullCallWrapper());
 
   // Invoke the JavaScript function in the given register. Changes the
   // current context to the context in the function before invoking.
   void InvokeFunction(Register function,
                       const ParameterCount& actual,
                       InvokeFlag flag,
-                      CallWrapper* call_wrapper = NULL);
+                      const CallWrapper& call_wrapper = NullCallWrapper());
 
   void InvokeFunction(JSFunction* function,
                       const ParameterCount& actual,
                       InvokeFlag flag,
-                      CallWrapper* call_wrapper = NULL);
+                      const CallWrapper& call_wrapper = NullCallWrapper());
 
   // Invoke specified builtin JavaScript function. Adds an entry to
   // the unresolved list if the name does not resolve.
   void InvokeBuiltin(Builtins::JavaScript id,
                      InvokeFlag flag,
-                     CallWrapper* call_wrapper = NULL);
+                     const CallWrapper& call_wrapper = NullCallWrapper());
 
   // Store the function for the given builtin in the target register.
   void GetBuiltinFunction(Register target, Builtins::JavaScript id);
 
   // Store the code object for the given builtin in the target register.
   void GetBuiltinEntry(Register target, Builtins::JavaScript id);
 
   // Expression support
   void Set(Register dst, const Immediate& x);
   void Set(const Operand& dst, const Immediate& x);
@@ skipping 446 matching lines @@
   // This handle will be patched with the code object on installation.
   Handle<Object> code_object_;
 
   // Helper functions for generating invokes.
   void InvokePrologue(const ParameterCount& expected,
                       const ParameterCount& actual,
                       Handle<Code> code_constant,
                       const Operand& code_operand,
                       NearLabel* done,
                       InvokeFlag flag,
-                      CallWrapper* call_wrapper = NULL);
+                      const CallWrapper& call_wrapper = NullCallWrapper());
 
   // Activation support.
   void EnterFrame(StackFrame::Type type);
   void LeaveFrame(StackFrame::Type type);
 
   void EnterExitFramePrologue();
   void EnterExitFrameEpilogue(int argc, bool save_doubles);
 
   void LeaveExitFrameEpilogue();
 
@@ skipping 118 matching lines @@
   }                                                                       \
   masm->
 #else
 #define ACCESS_MASM(masm) masm->
 #endif
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_IA32_MACRO_ASSEMBLER_IA32_H_